1. Field of the Invention
The present invention relates to an infrared ray detector and more particularly, relates to an infrared ray detector for detecting, e.g., the temperature of a portion to be detected by infrared rays.
2. Description of the Prior Art
FIGS. 1a and 1b show a side elevational view and a plan view of a conventional infrared ray detecting mechanism, respectively. In FIGS. 1a and 1b, a conventional infrared ray detector 1 contains an infrared ray detecting member of, e.g., a pyroelectric type. Such an infrared ray detecting member has a characteristic of generating electric charges based on changes in the amount of incident infrared rays, and the more the changes in the amount of the incident infrared rays are periodic, the more accuracy of detection by the infrared ray detecting member is improved. Accordingly, it is necessary to periodically change the amount of the infrared rays incident upon the infrared ray detecting member, and, to this end, arranged in front of the infrared ray detector 1 is a metal chopper 3 which is periodically driven to rotate by a synchronous motor 2. Thus, when infrared rays from the portion to be detected (not shown) and infrared rays from the chopper 3 alternately and periodically enter the infrared ray detecting member by rotation of the chopper 3, the infrared ray detecting member generates electric charges with the amount of incident infrared rays being periodically changed. Such electric charges are utilized for measuring the temperature of the portion to be detected.
However, in the structure as described in the foregoing, the motor 2 and the chopper 3 are considerably largely formed, and hence, the space for the infrared ray detecting mechanism itself becomes larger.
FIG. 2 shows a sectional view of an example of a conventional infrared ray detector which is formed to a smaller sized shape. Such infrared ray detector is disclosed in U.S. application Ser. No. 407,582 filed Aug. 12, 1982 now U.S. Pat. No. 4,485,305, by Kenichi Shibata et al. Such an infrared ray detector 4 is in the form of a small rectangular parallelepiped with external sizes of length, width and height of about 24 mm, 15 mm and 15 mm respectively, and contains a novel chopper mechanism. As a result, no provision of the motor 2 and chopper 3 is required, so that the space for an infrared ray detecting mechanism is reduced.
In addition, FIG. 3 is a plan view of an essential portion of the infrared ray detector 4 as shown in FIG. 2.
Referring to FIGS. 2 and 3, specific structure of the infrared ray detector 4 will be described in the following. In FIG. 2, in the interior of an outer case 8 consisting of a cap 7 having a header 5 of metal and an infrared ray transmitting portion 6, there are provided a pyroelectric type infrared ray detecting member 9 for generating electric charges based on changes in the amount of incident infrared rays and a chopper mechanism for changing the amount of the infrared rays incident upon the detecting member. The chopper mechanism, as shown in FIG. 3, comprises a pair of piezoelectric vibrating members 10 and 11 and a pair of opposing members 12 and 13 which are fixed to the respective ends of the vibrating members. Such opposing members 12 and 13 are respectively provided with a plurality of slits 14, 14 . . . which are identical in shape and size with each other for respectively transmitting the infrared rays.
If and when a driving signal is applied to a pair of piezoelectric vibrating members 10 and 11, the vibrating members 10 and 11 periodically vibrate mutually in opposite directions (directions A or B), whereby relative positional relation between the opposing members 12 and 13 is periodically changed accompanied by repetition of a state in which the respective slits 14, 14 . . . of the opposing members 12 and 13 are superposed to be most opened, i.e., to be completely opened and a state in which the respective slits 14, 14 are not superposed to be most blocked, i.e., to be completely blocked. Then, with the slits 14, 14 being superposed with each other, the infrared rays from a portion (not shown) to be detected enter the infrared ray detecting member 9 through the infrared ray transmitting portion 6 of the case 8 and the slits 14, 14 . . . of the opposing members 12 and 13 while, in the non-superposed state, only the infrared rays from the opposing members 12 and 13 enter the infrared ray detecting member 9. As a result, the amount of incident infrared rays to the infrared ray detecting member 9 periodically changes and the detecting member 9 generates electric charges used, e.g., for measuring the temperature of the portion to be detected.
In the above infrared ray detector 4, the vibrating members 10 and 11 are influenced by the ambient temperature to be deflected in the direction A or B due to the change in the ambient temperature. When the relative positional relation between the opposing members 12 and 13 in a steady state, i.e., in a non-vibrating state is changed by such deflection, no repetition of the states in which the slits 14, 14 . . . are completely superposed and the same are not in the least superposed is carried out upon vibration. As a result, the change in the amount of infrared rays incident upon the infrared ray detecting member 9 is decreased and thus the amount of the electric charges generated by the infrared ray detecting member 9 is decreased, leading to incorrect measurement of the temperature.
Consequently, it is necessary to make the relative positional relation between the opposing members 12 and 13 upon non-vibration not changed even if the ambient temperature is changed. There are two methods in this regard.
In a first method, previous study is made as to whether the vibrating members 10 and 11 are deflected in the direction A or in the direction B with respect to the change in the ambient temperature to arrange the vibrating members 10 and 11 for making the same deflected in the same direction, with the vibrating members 10 and 11 selected to be in the same structure and to have substantially same temperature coefficients in fine individual changes in the temperature coefficients. Consequently, the vibrating members 10 and 11 are deflected in the same direction substantially in the same amounts with respect to the change in the ambient temperature, whereby the relative positional relation between the opposing members 12 and 13 is not substantially changed.
In a second method, then, optimum bias signals are applied to the respective vibrating members 10 and 11 for supplying the respective vibrating members 10 and 11 with deflection in opposite directions to and in the same amount with the deflection that may be caused by the change in the ambient temperature. Consequently, the deflection of the respective vibrating members 10 and 11 that may be caused by the change in the ambient temperature is cancelled, whereby the relative positional relation between the opposing members 12 and 13 is not changed in the least.
However, in the former case, it is considerably difficult to select the vibrating members 10 and 11 to have substantially identical temperature coefficients, while in the latter case, it is considerably difficult to find out the optimum bias signals.